As Donald R. Kennedy described in “The History of Shaped Charges,” the concept of shaping an explosive charge to focus its energy was known as far back as 1792. In 1884, Max von Forester conducted experiments in Germany showing that an explosive charge with a hollow cavity will focus the explosive energy and produce a collimated jet of high speed gasses along the longitudinal axis of the cavity. When this cavity is lined with a ductile metal, it will produce a high speed collimated stretching jet of liquefied material capable of penetrating all known materials.
In 1888, Charles Munroe was conducting research for the U.S Navy at Newport, R.I., and he discovered that explosive energy could be focused in this manner and lining the hollow cavity in the explosive with metal increased the penetration dramatically. This effect is now commonly referred to as the “Munroe Effect.”
These discoveries were further studied in 1910 by Egon Neumann of Germany when he conducted similar experiments, and his experiments showed that a cylinder of explosive material with a metal lined hollow cavity could result in a shape charge jet stream that can penetrate steel plates. The military implications of this phenomenon were not realized until just prior to, and after, World War II.
In the 1930's, flash x-ray technology was developed that allowed the in-depth study of shaped charge jetting process. With this new diagnostic, it was possible to take X-Ray pictures of the collapse of the liner and the resulting jet. This new diagnostic tool led to a more scientific and complete understanding of the Munroe principle, and improved the techniques and power achieved by explosive shaped charges.
When an explosive shaped charge device is detonated, the energy of the explosive material can be focused into a rod-like jet of high temperature, high pressure and high velocity gases along the axis of the shape charge explosive device. The pressures created behind the detonation front in the explosive are of such magnitude that it causes the metal of the liner to liquefy and flow like a fluid. As the liner material is collapsed toward the axis of the hollow cavity, the flowing material radially converges, creating a rod-like stretching jet of high velocity, between five and ten kilometers per second.
Historically, these jets are composed of copper, and the conventional shaped charge will give typically create a hole size that is, in a semi-infinite target; could be as high as 20% of the diameter of the shaped charge. In order to achieve the greatest jet length and penetration depth, the jetting process of a shaped charge requires the liner material to reach a high temperature during collapse, which allows plastic flow of the collapsed liner material that produces a long stretching jet.
There have been some specialized efforts by Halliburton to produce shaped charges other than conical type shaped charges for special purposes such as pipe cutting and anchor chain cutting. These type of charges are called linear shaped charges and use the Munroe principle to produce a thin sheet like jet with somewhat similar cutting power to the usual conical shaped charge. The liner is wide angle and the device is used against light structures such as wooden doors and thin walls. The vast majority of research and development in shaped charges over the past hundred years or so has been devoted to deep penetration in both military and commercial applications. Some efforts have been directed to increasing the internal angle of the liner and a shorter standoff.
Other devices using flexible linear shaped charges have been designed for breaching man-size holes in light walls, such as described in Wall AXE British, 1960. These line charge devices are collapsed from only two opposing directions producing a very irregular thin sheet-like jet that is unpredictable in its penetrating ability due to the lack of a simultaneous initiation along the apex of the line explosive. These line charges are limited in the thickness or toughness of the target they can address and are mainly used for light walls.
U.S. Pat. No. 7,753,850 places an interrupter along the jet axis inside the liner, in the flow path of the liner material. The permissible size of the interrupter for this concept can only be a small portion of the liner diameter so as to leave room for the liner to collapse. The small diameter of the interrupter does not form a large enough diameter jet to produce a full caliber hole or to hold its annular shape after it separates from the interrupter; the jet will converge into a rod and some of the precious liner length is wasted.
U.S. Pat. Publ. No. US2011/0232519 A1 shows outside and inside walls making up the circular trough of the liner. The mass of the outer wall of the liner trough, because of its greater diameter, is much greater than the mass of the inner wall. The outer wall is converging whereas the inner wall, with much less mass, is diverging; the same problem exists with the explosive quantities driving each wall of the liner. To obtain a circular or annular jet, these masses must be equal in forces when they converge on the projected axis of the liner cavity.
In steel-making, small conical shaped charges are often used to pierce taps that have become plugged with slag. Linear shaped charges, or line charges, are another type of shaped charge used in the demolition of buildings to cut through steel beams and collapse the building in a desired pattern. This type of flexible line charge creates a sheet-like jet from a two-dimensional collapse.
SWAT teams and fire departments are another user of line charges, using the Munroe principle to generate high speed material for urban wall breaching and rescue. These line charges are very inefficient and difficult to initiate in a manner conducive to achieving their full potential. Additionally, sometimes users such as police or firefighters are badly injured or killed trying to use these awkward and clumsy devices.
Explosive hole or perforation diameters in casing from these conventional charges are not greater than ½ inch in diameter. The expected perforated holes sizes can be inconsistent, varying in size to more than 50% from the target diameter. This inconsistency causes many fracturing operation issues, and small hole size limits product flow into and from the formation; if too small, the perforation will get fouled with debris and can stop flowing altogether. The hole diameter produced by a present day oil well perforator is only approximately 12% of its explosive charge diameter. Great efforts have been made over the last 50 or so years to enlarge the entry hole diameter in oil well casing without much success.
Some effort has been made with placing a conventional shaped charge ahead of the projectile in order to create a pilot hole in the rock; however, only a small gain in depth of penetration is achievable with this method because of the very small hole diameter produced by a conventional shaped charge. The hole diameter made by a conventional shaped charge jet is small, on the order of one-tenth the diameter of the explosive charge forming the jet, and it penetrates approximately 6-8 times the diameter of the charge in steel (more in rock or masonry).
There have been many efforts throughout the years to hydraulically fracture resource bearing formations, but these prior efforts have been unable to penetrate more than a few feet beyond the main well bore. Present day stimulation of oil and gas bearing formations is most predominately accomplished by hydraulic fracturing (HF), also called “fracking.” Hydraulic fracturing (HF) is a time consuming multi-stage operation where the well bore is perforated with small holes or small perforations in the well casing and surrounding formation.
Although hydraulic fracturing of oil and gas bearing formations has been used for many decades, this process does not maximize the capture of valuable energy resources and it leaves valuable resources behind in the formation. During hydraulic fracturing (HF), fluids are forced into the formation through small holes or perforations in the well casing, which are formed during a perforation operation. These fluids include hydraulic fracturing fluids, which open fissures along natural lines of formation weaknesses or faults.
There are many problems associated with these hydraulic fracturing and the use of hydraulic fracturing fluids. First, the hydraulic fracturing fluids deposit proppants in the well perforations that initially maintain an open flow of fluids in the formation, but these proppants eventually grind down to powder and close up the formation fluid flow. This clogging and closure in the formation fluid flow causes production inefficiencies, which cannot be remedied by present hydraulic fracturing (HF) techniques.
Second, hydraulic fracturing (HF) can only create fracture lines that are not controlled by depth or direction, which means traditional hydraulic fracturing (HF) techniques cannot be regulated to target the highest resource bearing portion of a formation. This problem highlights one major problem with hydraulic fracturing (HF), which does not maximize the capture of valuable energy resources and leaves valuable resources behind in the formation based on this problem.
Third, traditional hydraulic fracturing (HF) techniques are very costly procedures, which consume approximately 80% of total well completion costs. The monetary costs makes traditional perforating techniques and hydraulic fracturing almost monetarily prohibitive at today's oil and gas prices.
Fourth, because hydraulic fracturing (HF) has no ability to be directional or depth controlled, the hydraulic fluids flow along formation fracture lines that follow planes of natural weaknesses in the formation material. This flow of high pressure hydraulic fracturing fluids into natural weaknesses in formation materials and formation fracture lines (e.g. faults) is accused of creating significant negative environmental impact and raised criticism and concerns about existing hydraulic fracturing (HF) techniques from the federal Environmental Protection Agency, as well as some state environmental agencies and environmentalists. Hydraulic fracturing (HF) techniques have been viewed under tighter and tighter scrutiny by these agencies and environmental advocates.
Previous efforts of energy recovery using traditional hydraulic fracturing techniques have not been successful or productive at increasing the production of energy resources from substrate formations around a borehole. In fact, the above problems will, in time, make the hydraulic fracturing (HF) operations more expensive to conduct (e.g. cost prohibitive), as well as less desirable and less practical, not to mention evoking environmental claims regarding the introduction of hydraulic fluids into fault areas of the surrounding formations, which individually or cumulatively may prevent and prohibit such uncontrolled and undirected hydraulic fracturing (HF) procedures. There is a legitimate need for an improved means of maximizing the development, recovery and production of energy resources by overcoming the existing and future problems inherent in uncontrolled and undirected hydraulic fracturing (HF) procedures.